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Insert Jacks... What, why and how


Steve Kennedy
Posted on Thursday, March 21, 2002 - 06:05 pm:   

Insert Jacks... What, Why & How

The front-panel Insert Jacks on the Music Man RD and RP series of amplifiers are essentially special-purpose access points into key parts of the signal chain, much like an effects loop.

To best use these jacks, you will need to construct or buy a special cable or adapter.

These jacks are Stereo TRS (Tip/Ring/Sleeve)1/4" , the stereo version of your standard 1/4" Phone plug found on your guitar cable.

The TIP connection is the INPUT to the following stages, the RING connection is the OUTPUT from the previous stages and the SLEEVE is GROUND.

A stereo 1/4" "headphone" plug to two mono 1/4" jacks is a relatively common adapter if you don't want to make or buy a special "insert" cable.

If you don't need one of the connections, then don't use it. Each jack has two connections (In & Out) and a unique signal level. Use only what you need when making a custom cable or modifying a standard cable with a new TRS plug.

For example, if you simply need a signal feed out of the amp (a line out) without disturbing the amp's signal path, then take a normal guitar cable and replace one end with a Stereo 1/4" plug. Wire the TIP to the RING and connect the RING to the center conductor of the cable, Sleeve connection to the ground shield of the cable. This cable will not stop the amp from working but will give you a signal output (either 100mV or 3V in level) depending on which jack you plug it into! Drive an effects rack and stereo amp for stereo effects or another Music Man amp!

Besides the difference in input/output levels, these jacks are ALSO located at different places in the circuitry of the 65 & 100 watt versions of these amps.

The 100mV jack is located AFTER the input preamp and tone controls, but BEFORE the Channel Switching, Distortion and Reverb (or Phasor on an RP model) stages on the 100 watt models.

The 3 Volt jack is located AFTER the Channel Switching & Distortion, but prior to the Reverb, and Phasor sections on the 100 watt models. These jacks are also before the Master Volume control.

On the 65 watt models (older series with relay switching of controls) both jacks are AFTER the Reverb & Phasor and just prior to the output amplifier.

It must be said that Music Man's choice of levels for these insert points can be a bit awkward for some applications. Standard Line Level is typically 1 volt. 100mV is higher than typical passive instrument level, but much lower than line level. 3 volts is a high Line Level signal that can overload a device unless it has an input gain control (or you ad one in the cable).

So, if you want to connect effects in an "effects loop", you will typically need to use the 100mV jack (but you can use the 3 volt jack if your effect device has an input level control).

If you want to access ONLY the output amplifier, you will want to use the 3 Volt jack and drive it with a larger signal (like the output of a preamp). This jack is typically used to slave multiple Music Man amps together from a single amp's preamp section.

You could also wire the 3 volt jack to a volume pedal for a remote Master Volume control for your amp.

Get the model number of your amp from the rear plate and download the proper schematic for your model if you want any more technical info on this.

You can buy cables premade for this application from most Music Shops that carry recording cables. These are called "TRS Insert Cables".

While some circumstances will allow you to plug a standard "Mono" guitar plug into the jack (but only about 1/2 to 2/3 the way in so you don't short out the RING connection to Ground), this can cause problems if not done properly.


(Message edited by admin on March 21, 2002)

(Message edited by admin on March 22, 2002)
Posted on Wednesday, June 12, 2002 - 10:25 am:   

Neato..um is it ok to use a mik in guitar port while playing guitar? also can you use a bass and guitar at the same time?
Steve Kennedy
Posted on Thursday, June 13, 2002 - 11:15 am:   

Microphones have very low output levels and will not alwyas work well in a guitar amp. High-level, high-impedance microphone's can work because these types have about the same output as a guitar pickup.

If your amp has two input channels (i.e. Normal & Bass)you could plug a guitar & bass into their own channels but you have to worry about whether your speakers can handle the bass. If you keep it low volume it should be OK (like at an intimate practice session in a quiet room).

I would not suggest plugging in two devices into a single channel... you won't break anything but it probably will not work well nor sound good.


Brad Harris
Posted on Monday, June 17, 2002 - 04:03 pm:   

could you explain more about how to wire the 3 volt jack as a volume pedal. Is it the a TRS on the amp end split out to two monos to the input and output of a standard volume pedal?
Steve Kennedy
Posted on Wednesday, June 19, 2002 - 02:43 pm:   

Yes! Using a standard TRS Insert cable, you would have 2 Mono TS 1/4" plugs available as IN & OUT for the volume control or whatever device you wanted to use it with.

Dave Cast
Posted on Monday, February 10, 2003 - 09:49 am:   

Do you (or others) prefer to run your effects through the effects loop or straight into the input? I have never used the loop before and would like to know how well it works.

Steve Kennedy
Posted on Sunday, March 16, 2003 - 01:23 am:   

It all depends what kind of effects you have. But before we go into that, I want to mention that there is a certain "relationship" that occurs between a guitar's pickup(s) and the amplifier input when connected directly together that almost never occurs when you insert an electronic circuit between them.

There is a certain tone and dynamic relationship that gets killed by using pedals and effects between the guitar and the preamp input. This was why effects loops were added to amplifiers in the first place. It may make less of a difference if you are playing heavy-metal with a high-gain amp, but the concept applies universally all the same.

Music Man tried to address this with the design of their RD & RP amplifiers. The 100mV "insert Jack" provides a "pedal" level effects loop while the 3V jack provides a "line level" effects loop for rackmount or studio effects units.

This is why many amps made today have send & receive volume controls for their effects loops... they allow the loop signals to be tailored for any type and combination of outboard equipment to be inserted in the signal chain without disturbing that "magic" relationship of a guitar and its preamp input!

Dave Cast
Posted on Monday, March 31, 2003 - 11:58 am:   

Thanks for the response. I am going to try running my pedalboard through the 100mV loop because I am noticing a signal loss in my clean sound when using the pedalboard.

Dave Cast
Posted on Friday, April 04, 2003 - 11:17 am:   

I tried running my effects through the 100mV loop and when I switch my board on the level dropped to about half of normal volume. Any ideas as to what I may be doing wrong?

Steve Kennedy
Posted on Friday, April 04, 2003 - 01:10 pm:   

I probably should have been more accurate in my statements. The 100mV jack WAS intended to be pedal-level, but probably as compared to a low output single-coil guitar pickup. More modern high-output (and humbucking) pickups put out about 3-5X this amount of signal.

You can either boost this signal with a micro-amp or preamp pedal ahead of the rest, turn up the Master to compensate (if noise is not a problem and there is enough range to the Master Volume Control) or crank more input Volume to drive the effects chain harder.

Probably the most effective would be to crank the input section Volume control (not too much Gain control or you will get more distortion than you want) to drive the pedals harder, then set your Master to get the volume you need.

This is the reason why most modern amps give you effects loop input and output pots, so you can optimize the amp for your setup. Since MM didn't do that for you, you need to modify your gain structure to best use the devices you have with your amp.

Just remember, too much input drive to your pedals will result in distortion, too little drive will result in higher noise. You want to figure out what settings give you a middle ground so that it works over a good range without noise or distortion.

John Lynch
Posted on Monday, April 07, 2003 - 01:48 am:   

I have a music man 112 RP-65 and would like to know if you can somehow use the lo level line in/out and hi level in/out jacks to bypass the solid state preamp with some type of a tube pedal.
Maybe this would not work at all because of the
impedance of the pedal. Thanks.
Steve Kenendy
Posted on Wednesday, April 16, 2003 - 08:57 am:   

If your external devices (i.e. tube preamp or pedal) can drive a large enough output signal, then use the 3V insert jack.

A signal applied at the input section of the 3V Insert Jack will go through the Master Volume control then straight into the output stage power amp.

In all Music Man amps, there will be at least some solid state devices in the signal path (phase splitter on later models and driver transistors on all models) but the entire preamp stage will be bypassed.

John Lynch
Posted on Wednesday, April 16, 2003 - 02:23 pm:   

Thanks so much for your help on this and other questions I have asked.
John Lynch
Posted on Thursday, April 17, 2003 - 02:05 am:   

So to bypass the preamp on the 112-RP-65 I couldn't just use a guitar cord, but would have to get a TRS plug and wire the Tip to the center conductor and the Sleeve connection to the ground shield of the cable and plug this into the 3 volt in/out jack. I think, right.
Steve Kennedy
Posted on Wednesday, April 23, 2003 - 01:23 pm:   

In reality, since your intention is to bypass the amp's own preamp and simply apply external drive audio to the power amp (at the Tip and Sleeve connections), using a standard 2-conductor phone jack as found on a standard guitar cable WOULD work in this instance.

You would be grounding out the output of the amplifier preamp stages, but since you will not be trying to use that circuitry it shouldn't make any difference.

To be on the safe side, I would turn all preamp volume and gain controls to "0" but other than that I don't see a particular problem.

Ed Goforth (ed_goforth)
Username: ed_goforth

Registered: 06-2006
Posted on Wednesday, August 15, 2007 - 02:15 am:   

I have a RD-100 and am having thoughts of rewiring the effects patch points to be after the master volume, but this may be quite intense of a mod... I tried it once and it made a big improvement, but I need to go into it again and see what I can do. Its kind of the like the Clapton mod, where the loop is before the master volume and that causes overload in the effects, having the loop after the master would be more like a effects send control, and possibly reconfiguring the opamps for better buffering. Just a thought.
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Saturday, November 07, 2009 - 03:36 am:   

ok,here is a question not brought up and I would love to know before experimenting and messing something up,1.can both the 100mv plug and the 3v plug be used at the same time?like running regular floor stompboxs though the 100mv and rack type stuff though the 3v.2.how hard would it be to change the values of the inputs ,like making the 100mv a 1v and maybe lowering the 3v.
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Saturday, June 26, 2010 - 08:06 am:   

does nobody have a thought on this ?i only been waiting 2 years for a response,lol
Crispin Gill (cris)
Username: cris

Registered: 06-2010
Posted on Sunday, July 04, 2010 - 04:59 pm:   

I have a 112 RP-65 and use the 100mv in/out for floor pedals and the 3v in/out for a rack FX (Alasis Microverb) at the same time with no problems. I use the volume control on the individual pedals & rack FX to set the level so it matches the same volume when they are disconnected, that way there is no level difference when they are connected and on. Check out the 'Manual' for more uses. I don't know about changing the values of these in/out's.